Digitization apparatus

ABSTRACT

The digitization apparatus includes, as a main scale, a pulse delay circuit constituted by a plurality of delay units connected in series or in ring form, a latch/encoder, a circulation number counter, and a latch circuit, and includes, as a vernier, a reverse timing extraction circuit detecting a reverse timing at which any one of the delay units has reversed, and an interpolation circuit. The main scale digitizes a time interval between two successive measurement signals in a resolution equal to a delay time per one delay unit. The vernier digitizes a time difference between a measurement timing indicated by the measurement signal and the reverse timing in a resolution equal to 1/M (M being an integer not smaller than 2). The interpolation circuit includes two delay lines each constituted by a plurality of delay units connected in series or in ring form.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to Japanese Patent Applications No.2006-135624 filed on May 15, 2006, and No. 2006-181652 filed on Jun. 30,2006, the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a digitization apparatus used fordigitizing a signal level of an analog signal, time intervals of pulsesignals, etc.

2. Description of Related Art

One example of such a digitization apparatus is a TAD-type A/D converter(referred to simply as “TAD” hereinafter) all the parts of which areconstituted by a digital circuit.

As described, for example, in Japanese Patent Application Laid-open No.5-259907, the TAD includes a pulse delay circuit constituted by aplurality of delay units connected in series or in ring form. The delaytime of these delay units depends on an operating voltage thereof. TheTAD outputs the number of the delay units which a pulse signal passesthrough in a predetermined measuring time period as digitization data(A/D converted data) representing a voltage of an analog input signalapplied to these delay units as their operating voltage.

That is to say, the TAD is configured such that a traveling speed of thepulse signal traveling through the pulse delay circuit is varieddepending on the analog input signal applied to the delay units as theiroperating voltage, and this traveling speed is measured by counting thenumber of the delay units which the pulse signal passes through in thepredetermined measuring time period.

The TAD can be used also as a time measuring apparatus capable ofoutputting data representing a length of elapsed time in digitized form,if a constant voltage signal is applied to the delay units as the analoginput signal to set the delay time of the delay units at a knownconstant value.

In the TAD, to increase the resolution of its output digitization data(A/D converted data), the delay time of each one of the delay units hasto be made shorter, or the measuring time period has to be made longerwhen the TAD is used as an A/D converter apparatus.

However, making the delay time of each delay unit has limitations,because the delay time is determined by a miniaturization level (CMOSdesign rule) of elements constituting the delay unit (gate circuits suchas an inverter, for example). In addition, when it is required to drivethe TAD by a low voltage for electric power saving, the delay time ofthe delay unit is restrained by this low driving voltage.

Furthermore, in a system using the TAD for performing A/D conversion athigh speed (several MHz to several tenth of MHz, for example), it is notpossible to lengthen the measuring time period to increase theresolution.

Incidentally, there is known a parallel-type (or flash-type) A/Dconverter capable of performing A/D conversion at high speed. However,the parallel-type A/D converter has to produce a number of referencevoltages by use of analog circuits depending on the resolution required.Accordingly, in the case of the parallel-type A/D converter, increasingits output resolution causes its circuit scale to increase, andaccordingly causes its production cost to increase.

SUMMARY OF THE INVENTION

The present invention provides a digitization apparatus comprising:

a pulse delay circuit constituted by a plurality of pulse delay unitsconnected in series or in ring form, each of the pulse delay unitshaving a delay time depending on a voltage level of an analog inputsignal applied thereto as a drive voltage thereof, the pulse delaycircuit allowing a pulse signal to travel through the pulse delay unitswhile being successively delayed by the delay time;

a higher coding circuit generating, upon receiving a measurement signalindicating a measurement timing from outside, digitized datarepresenting the number of the pulse delay units which the pulse signalhas passed;

a reverse timing extraction circuit extracting a timing, as a reversetiming signal, at which any one of the pulse delay units has reversed inoutput level for the first time after the measurement timing;

a first delay line constituted by a plurality of first delay unitsconnected in series or in ring form, each of the first delay unitshaving a first delay time, the first delay line allowing the reversetiming signal to travel through the first delay units while beingsuccessively delayed by the first delay time;

a second delay line constituted by a plurality of second delay unitsconnected in series or in ring form, each of the second delay unitshaving a second delay time larger than the first delay time by 1/M (Mbeing an integer not smaller than 2) of the delay time of the pulsedelay units, the first delay line allowing the reverse timing signal totravel through the second delay units while being successively delayedby the second delay time; and

a lower coding circuit generating digitized data representing a timedifference between the measurement timing and the reverse timing on thebasis of the number of the first delay units which the reverse timingsignal has passed when the number of the first delay units has overtakenthe number of the second delay units which the measurement signal haspassed;

the digitization apparatus outputting data formed by the digitized datagenerated by the higher coding circuit as higher bits thereof, and thedigitized data generated by the lower coding circuit as lower bitsthereof.

According to the present invention, it is possible to provide adigitization apparatus constituted only by digital circuits, and capableof digitizing a signal level of an analog signal, or time intervalsbetween successive pulse-like signals at high speed and in highresolution without using any complicated analog circuits.

The first delay units and the second delay units may be applied with theanalog input signal as a drive voltage thereof.

The digitization apparatus may further comprise a time measurementcontrol apparatus generating a constant voltage signal as the analoginput signal, and a start signal to cause the pulse signal to starttraveling through the pulse delay units of the pulse delay circuit, thedigitization apparatus outputting data representing in digitized form atime interval between a start timing indicated by the start signal andthe measurement timing each time the measurement signal is inputted tothe higher coding circuit.

The digitization apparatus may further comprise an A/D conversioncontrol circuit supplying the higher coding circuit with the measurementsignal at predetermined constant periods, the digitization apparatusoutputting, at the measurement timing indicated by measurement signal,data representing a voltage level of the analog input signal indigitized form.

The digitization apparatus may further comprise a differentialcalculating circuit successively memorizing output data generated by thedigitization apparatus, and calculating a difference between the outputdata generated previous time and the output data generated this time.

The lower coding circuit may include an edge detection circuitconstituted by a plurality of flip-flop circuits provided in one-to-onerelationship with the first delay units and the second delay units, eachthe flip-flop circuit receiving an output of a corresponding one of thefirst delay units at one of a data input terminal and a clock inputterminal thereof, and receiving an output of a corresponding one of thesecond delay units at the other of the data input terminal and the clockinput terminal thereof, an encoder generating stage-number datarepresenting in digitized form a stage number of one of the flip-flopcircuits which has changed an output level thereof, and a dataconversion circuit converting the stage-number data to such data whosevalue monotonously increases with increase of a time difference betweenthe reverse timing and the measurement timing.

The data conversion circuit may perform at least one of elimination ofoffset contained in the stage-number data, and correction of a gainerror of the stage-number data.

The digitization apparatus may further comprise a test signal generatingcircuit having a function of generating the analog input signal, andgenerating the measurement signal in continuously changing period, and acorrection data calculating circuit calculating correction data neededfor the data conversion circuit to perform elimination of the offset orcorrection of the gain error on the basis of the stage-number dataoutputted from the encoder when the digitization apparatus operates onthe analog input signal, and the measurement signal generated by thetest signal generating circuit.

A delay circuit having the same characteristic with respect to at leastone of drive voltage and ambient temperature with the pulse delay unitsmay be provided in an input side of the second delay line.

The digitization apparatus may further comprise a first D/A convertergenerating, from adjustable digital set value, an adjustable drivevoltage to be supplied to the first delay units, and a second D/Aconverter generating, from adjustable digital set value, an adjustabledrive voltage to be supplied to the second delay units.

Each of the pulse delay units may be constituted by a series connectionof a plurality of inverter gate circuits.

The inverter gate circuit may be a CMOS inverter gate circuit. In thiscase, preferably, the drive voltage of the pulse delay unit is set at avalue smaller than a sum of a threshold voltage of an N-channeltransistor and a threshold voltage of a P-channel transistor, whichconstitute the CMOS inverter gate circuit.

The reverse timing extraction circuit may include latch circuitslatching the measurement signal respectively in synchronization withoutputs of the pulse delay units constituting the pulse delay circuit,and an OR circuit outputting a logical sum of outputs of the latchcircuits as the reverse timing signal.

Other advantages and features of the invention will become apparent fromthe following description including the drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1A is a block diagram showing an overall structure of a timemeasuring apparatus including a digitization section according to afirst embodiment of the invention;

FIG. 1B is a timing diagram showing the operation of the time measuringapparatus shown in FIG. 1A;

FIG. 2 is a block diagram showing a structure of the digitizationsection shown FIG. 1A;

FIG. 3 is a diagram explaining a structure of a delay unit constitutinga pulse delay circuit included in the digitization section shown in FIG.2;

FIG. 4 is a circuit diagram of a reverse timing extraction circuitincluded in the digitization section shown in FIG. 2;

FIG. 5 is a diagram showing a structure of an interpolation circuitincluded in the digitization section shown in FIG. 2;

FIG. 6 is a timing diagram explaining the operation of the interpolationcircuit shown in FIG. 5;

FIG. 7 is an explanatory view showing a relationship among stage-numberdata, reverse timing, and measurement timing;

FIG. 8 is an explanatory view explaining the operation of a dataconversion circuit included in a lower coding section included in theinterpolation circuit shown in FIG. 5;

FIG. 9 is a circuit diagram of a variant of the reverse timingextraction circuit included in the digitization section shown in FIG. 2;

FIG. 10 is a block diagram showing an overall structure of a timemeasuring apparatus including a digitization section according to asecond embodiment of the invention;

FIG. 11 is a block diagram showing a structure of digitization sectionincluded in a time measuring apparatus according to a third embodimentof the invention;

FIG. 12 is a circuit diagram showing a structure of a latch/reversetiming extraction circuit included in the digitization section shown inFIG. 11;

FIG. 13 is a circuit diagram showing a structure around a first delayline and a second delay line of an interpolation circuit of adigitization section included in a time measuring apparatus according toa fourth embodiment of the invention;

FIG. 14 is a circuit diagram showing an overall structure of aninterpolation circuit of a digitization section included in a timemeasuring apparatus according to a fifth embodiment of the invention;

FIG. 15A is a block diagram showing an overall structure of an A/Dconversion apparatus including a digitization section according to asixth embodiment of the invention;

FIG. 15B is a timing diagram showing the operation of the A/D conversionapparatus shown in FIG. 15A; and

FIG. 16 is a block diagram showing a structure of a calibration circuitprovided in a time measuring apparatus or an A/D conversion apparatusincluding a digitization section according to a seventh embodiment ofthe invention.

PREFERRED EMBODIMENTS OF THE INVENTION First Embodiment

FIG. 1A is a block diagram showing an overall structure of a timemeasuring apparatus 1 including a digitization section 10 according to afirst embodiment of the invention. FIG. 1B is a timing diagram showingthe operation of the time measuring apparatus 1.

As shown in this figure, the time measuring apparatus 1 is constitutedby the digitization section 10 and a time measurement control section 3.The time measurement control section 3 generates an analog input signalVin of constant voltage (5V, in this embodiment), and a start signal PAwhich changes from a non-active level (low level in this embodiment) toan active level (high level in this embodiment) in response to a startcommand supplied from the outside of the time measuring apparatus 1. Thedigitization section 10 receives, in addition to the analog input signalVin of constant voltage and the start signal PA generated by the timemeasurement control section 3, a pulse-like measurement signal PB whichrises at measurement timings Ti (i=1, 2, 3 . . . ) as shown in FIG. 1B.The digitization section 10 is configured such that, when being suppliedwith the measurement signal PB after the start signal PA has changed tothe active level at a start timing Ts, the digitization section 10measures a time interval between the start timing Ts and a firstmeasurement timing T1, or a time interval between a previous timemeasurement timing Ti−1 and this time measurement timing T1, and outputsdata DT representing the measured time interval in digitized form.

FIG. 2 is a block diagram showing a structure of the digitizationsection 10. As shown in this figure, the digitization section 10includes a pulse delay line 11, a latch/encoder 12, a circulation numbercounter 15, and a latch circuit 16. The pulse delay line 11 isconstituted by L (L=2^(b), b being a positive integer) delay units DUconnected in ring form to operate as a ring delay line through which apulse signal circulates when the start signal PA is inputted, each ofthe delay units DU delaying its input signal (the pulse signal) by adelay time Td. The latch/encoder 12 latches the outputs P1 to PL of thedelay units DU at the measurement timing Ti of the measurement signalPB, and outputs b-bit digital data (may be referred to as “middle data”hereinafter) DM representing in what stage number of the delay units DUthe pulse signal is. The circulation number counter 15 is a c (c being apositive integer)-bit counter counting the output (the circulating pulsesignal) of a final stage delay unit DU. The latch circuit 16 operates tolatch the count value of the circulation number counter 15 at themeasurement timing, and outputs c-bit digital data (may be referred toas “higher data” hereinafter) DH representing the latched count value.

As shown in (a) of FIG. 3, each of the delay units DU is a buffercircuit constituted by a serial connection of two CMOS inverter gatecircuits, with exception that the first stage delay unit DU isconstituted by an AND gate circuit one of two input terminals of whichis a starting terminal.

The other input terminal of the first stage delay unit DU is connectedto an output terminal of the final stage delay unit DU so that the delayunits DU form a ring delay line. Although not shown in the figures, thepulse delay circuit 11 has means for adjusting the signal level at theinput terminal of the first stage delay unit DU to enable the pulsesignal to continue to circulate in the pulse delay circuit 11. Since thestructure of the pulse delay circuit as described above is disclosed indetail, for example, in Japanese Patent Application Laid-open No.6-216721, further explanation thereof is omitted here.

Each of the delay units DU is applied with, as its drive voltage, theanalog input signal Vin supplied from the time measurement controlsection 3 through a buffer circuit 18. Accordingly, the delay time ofeach delay unit DU varies depending on the voltage level of the analoginput signal Vin.

However, in this embodiment, the voltage level of the analog inputsignal Vin is kept constant, and accordingly, the delay time of eachdelay unit DU is constant. Therefore, the number of the delay units DUwhich the pulse signal passes through varies in proportion to a timeperiod between the start timing Ts and the measurement timing Ti.

The pulse delay circuit 11 further includes a reverse timing extractioncircuit 13, an interpolation circuit 14, and a differential calculatingcircuit 17. The reverse timing extraction circuit 13 generates a reversetiming signal PR representing a timing at which any one of the outputsP1 to PL of the delay units DU has reversed for the first time since themeasurement signal PB was inputted. The interpolation circuit 14 outputsa-bit (a being a positive integer) digital data DL (may be referred toas “lower data” hereinafter) representing a time differential between areverse timing indicated by the reverse timing signal PR and ameasurement timing indicated by the measurement signal PB in aresolution M (M=2^(a),) times finer than the middle data DM outputtedfrom the latch/encoder 12. The differential calculating circuit 17successively memorizes, as absolute value data DA representing the timeinterval between the start timing Ts and the measurement timing Ti,N-bit data (N=a+b+c) which is formed by the lower data DL received aslower bits from the interpolation circuit 14, the middle data DMreceived as middle bits from the latch/encoder 12, and the higher dataDH received as higher bits from the latch circuit 16, calculates adifference between the absolute value data DA memorized at previous timeand the absolute value data DA memorized this time, and generates N-bitdata DT representing a time interval between the preceding measurementtiming Ti−1 and the current measurement timing Ti.

As shown in FIG. 4, the reverse timing extraction circuit 13 includes Lflip-flop circuits DFF, an OR circuit OR, and an enabling signalgenerating circuit 19. The L flip-flop circuits DFF commonly receive themeasurement signal PB at their data input terminals, and respectivelyreceive the outputs P1 to PL of the delay units DU constituting thepulse delay circuit 11 at their clock input terminals. The OR circuit ORreceives the outputs of the L flip-flop circuits DFF, and generates thereverse timing signal PR to be supplied to the interpolation circuit 14.The enabling signal generating circuit 19 generates an enabling signalEN which causes the flip-flop circuits DFF to reset their outputs at therising edge of the measurement signal PB (that is, at the measurementtiming Ti), and causes the flip-flop circuits DFF to perform their latchoperations until the reverse timing signal PR rises.

As understood from the above, the reverse timing signal PR rises at atiming when any one of the outputs of the flip-flop circuits DFF risesfor the first time (actually, it is lagged due to the delays in theflip-flop circuits DFF and the OR circuit OR) after the measurementsignal PB rises (that is, after the current measurement timing Ti), andstays in this state until the measurement signal PB rises next (untilthe succeeding measurement timing Ti+1).

As shown in FIG. 5, the interpolation circuit 14 includes a first delayline 21, a second delay line 22, an edge detection circuit 23, and alower coding section 24. The first delay line 21, which is constitutedby a series connection of P (P≧M) delay units DU1 each of which delaysits input signal by a predetermined delay time Td1, receives the reversetiming signal PR outputted from the reverse timing extraction circuit13. The second delay line 22, which is constituted by a seriesconnection of P delay units DU2 each of which delays its input signal bya predetermined delay time Td2, receives the measurement signal PB. Theedge detection circuit 23 is constituted by P flip-flop circuits DFF,the p-th stage (p=1,2, . . . , P) flip-flop circuit receiving the outputDp of the p-th stage delay unit DU1 of the first delay line 21 at itsdata input terminal, and receiving the output CKp of the p-th stagedelay unit DU2 of the second delay line 22 at its clock input terminal.The lower coding section 24 generates the lower data DL representing thetime differential between the measurement timing and the reverse timingon the basis of the outputs QV1 to QVP of the flip-flop circuits DFFconstituting the edge detection circuit 23.

Although not shown in this figure, the delay units DU1 constituting thefirst delay line 21 and the delay units DU2 constituting the seconddelay line 22 are applied with the analog input signal Vin as theirdrive voltage like the delay units DU constituting the pulse delaycircuit 11.

The delay time Td2 of the delay units DU2 constituting the second delayline 22 is larger than the delay time Td1 of the delay units DU1constituting the first delay line 21 by 1/M of the delay time Td of thedelay units DU constituting the pulse delay circuit 11.

That is, the following equation (1) holds.Td2=Td1+Td/M  (1)

In this embodiment, Td1 equals to Td, and M equals to 16 (that is, a=4).

As shown in FIG. 6, the reverse timing signal PR is inputted to thefirst delay line 21 at a timing lagging behind a timing at which themeasurement signal PB is inputted to the second delay line 22 (thelagging time is not larger than the delay time Td). Since the delaytimes of the delay units DU1 and DU2 are in the relationship shown inthe equation (1), the delayed pulse resulting from the reverse timingsignal PR (may be referred to as a first delay pulse hereinafter)overtakes the delayed pulse originating from the measurement signal PB(may be referred to as a second delay pulse hereinafter) at a momentwhen it passes through the M-th stage delay unit DU1.

At this time, the output QVp of the p-th stage flip-flop circuit DFFconstituting the edge detection circuit 23 is at the low level if thedelayed pulse on the first delay line 21 does not yet overtake thedelayed pulse on the second delay line 22, and otherwise at the highlevel.

Returning back to FIG. 5, the lower coding section 24 includes anencoder 25, and a data conversion circuit 26. The encoder 25 generatesstage-number data representing the numbers of the delay units DU1 andDU2 which the above first and second delay pulses have passed before thefirst delay pulses overtakes the second delay pulse on the basis of theoutputs QV1 to QVp of the flip-flop circuits DFF of the edge detectioncircuit 23. The data conversion circuit 26 corrects the stage-numberdata generated by the encoder 25 to generate the lower data DL.

The data conversion circuit 26 is constituted by a memory 27, asubtracter 28, and a divider 29. The memory 27 is for storing offsetdata and division data to be explained later. The subtracter 28 is forsubtracting the stage-number data DD generated by the encoder 25 fromthe offset data stored in the memory 27. The divider 29 is for dividingthe subtraction result (may be referred to as “first correction dataHD1” hereinafter) of the subtracter 28 by the division data stored inthe memory 27. The data conversion circuit 26 outputs a division result(may be referred to as “second correction data HD2” hereinafter) of thedivider 29 as the lower data DL.

Hence, as shown in FIG. 7, the stage-number data DD generated by theencoder 25 takes its minimum value DDmin when a reverse timing Tr atwhich any one of the outputs of the delay units DU reverses (at thetiming at which the LSB of the middle data DM reverses), and themeasurement timing Ti agree with each other, and takes its maximum valueDDmax at a moment when the measurement timing Ti lags behind the reversetiming Tr. As this time lag increases, in other words, when the timelead of the measurement timing Ti with respect to the reverse timing Trdecreases, the stage-number data DD decreases. That is, the value of thestage-number data DD varies in sawtooth wave form with the change of themeasurement timing Ti.

The minimum value DDmin becomes 0, if the reverse timing Tr and an inputtiming at which the reverse timing signal PR is inputted to the firstdelay line 21 exactly coincide with each other. Actually, since theinput timing lags behind the reverse timing due to the presence of thereverse timing extraction circuit 13, the minimum value DDmin does notbecome 0, that is, the so-called offset arises.

The difference between the maximum value DDmax and the minimum valueDDmin is equal to M−1 if the delay time difference ΔT (=Td2−Td1) betweenthe delay time of the delay unit DU1 and the delay time of the delayunit DU2 is exactly equal to Td/M. If ΔT>Td/M, DDmax−DDmin≧M−1, and ifΔT<Td/M, DDmax−DDmin≦M−1. Hence, an error of the delay time differenceΔT becomes a gain error of the stage-number data DD, which changes theslope of the stage-number data DD shown in FIG. 7.

Since the value of the stage-number data DD decreases as the time lag ofthe measurement timing Ti with respect to the reverse timing Trincreases, it has to be converted such that its value increases as thetime lag increases to generate the lower data DL.

Accordingly, the data conversion circuit 26 obtains the first correctiondata HD1 having the characteristic shown by the straight line B in FIG.8 in accordance with the following equation (2) using the maximum valueDDmax as the offset data, so that the offset is removed, and thestage-number data DD having the characteristic shown by the straightline A in FIG. 8 is converted such that its value monotonously increaseswith the increase of the time lag of the measurement timing Ti withrespect to the reverse timing Tr.HD1=DDmax−DD  (2)

In addition, the data conversion circuit 26 further obtains the secondcorrection data HD2 having the characteristic shown by the straight lineC in FIG. 8 in accordance the following equation (3), so that the firstcorrection data HD1 having the characteristic shown by the straight lineB in FIG. 8 is converted such that the lower data DL is in a value rangefrom 0 to M−1.HD2(=DL)=HD1×M/(DDmax−DDmin)  (3)

Incidentally, since the maximum value DDmax of the stage-number data DDvaries depending on the offset and the gain error, it is necessary todetermine the stage numbers of the delay units DU1, DU2 taking accountof the offset and the gain error.

As explained above, the time measuring apparatus of this embodiment,which includes, as a main scale, the pulse delay circuit 11, thelatch/encoder 12, the circulation number counter 15 and the latchcircuit 16, and includes, as a vernier, the reverse timing extractioncircuit 13 and the interpolation circuit 14, measures (digitizes), byuse of the main scale, the time interval between the two successivemeasurement timings of the signals PB in a resolution equal to the delaytime of each one of the delay units DU, and measures (digitizes), by useof the vernier, the time interval between the reverse timing Tr of thedelay units DU and the measurement timing in a resolution M times finerthan the resolution of the main scale.

The interpolation circuit 14, which includes the first delay line 21constituted by the plurality of the delay units DU1 each having thedelay time Td1, and the second delay line 22 constituted by theplurality of the delay units DU2 each having the delay time Td2 which islarger than the delay time Td1 by ΔT (=Td/M), is configured such thatthe resolution of the vernier is determined not by the delay times ofthe delay units DU1, DU2, but by the delay time difference ΔT betweenthe delay time of the delay unit DU1 and the delay time of the delayunit DU2.

According to this embodiment, it is possible to digitize the timeintervals of the successive measurement timings of the measurementsignals PB at high speed and in high resolution without using anycomplicated analog circuits and the CMOS design rule fine patterns.

In this embodiment, as shown in FIG. 4, the reverse timing extractioncircuit 13 is constituted by the flip-flops DFF, the OR circuit OR, andthe enabling signal generating circuit 19. However, this reverse timingextraction circuit 13 have a problem in that the flip-flop circuits DFFmay become unstable depending on a timing at which the measurementsignal PB applied to the data input terminals thereof changes its value.This causes the delay time of the flip-flop circuits DFF to vary, whichprevents the reverse timing extraction circuit 13 to stably output thereverse timing signal PR.

To cope with this problem, instead of the reverse timing extractioncircuit 13 shown in FIG. 4, a different reverse timing extractioncircuit 13 a shown in FIG. 9 may be used. As shown in this figure, thereverse timing extraction circuit 13 a additionally includes flip-flopcircuits DEF_E disposed in the rear of the flip-flop circuits DEF in aone-to one relationship. Each flip-flop circuit DEF_E is applied withthe output of the corresponding flip-flop circuit DEF at its data inputterminal, applied with, at its clock input terminal, one of the outputsP1 to PL, which is phase-shifted by 180 degrees with respect to anotherone of the outputs P1 to PL applied to a clock input terminal of theflip-flop-circuit DFF preceding to this corresponding flip-flop circuitDEF, and applied with the inverted version of the output of the ORcircuit OR (that is, reverse timing signal PR) at its enable inputterminal. The outputs of the flip-flop circuits DEF_E are inputted tothe OR circuit OR. The reverse timing extraction circuit 13 a may beconfigured such that the enable signal EN is applied to a selected oneof the flip-flop-circuits DFF and the flip-flop circuits DEF_E.

In the reverse timing extraction circuit 13 a, the delay time variationof the flip-flop circuits DFF on the front side does not affect thereverse timing signal PR. The time lag of the reverse timing signal PRwith respect to the reverse timing shown by the outputs of the delayunits DU increases by the delay time of the flip-flop circuits DEF_Eonthe rear side. However, since the delay time of the flip-flop circuitsDEF_E is made constant, it is possible to cause the interpolationcircuit 14 to generate the lower data DL with a high degree of accuracyby providing a delay circuit having the same constant delay time as theflip-flop circuits DEF_E for delaying the measurement signal PB.

In the case where the delay unit DU is constituted by CMOS inverter gatecircuits, the drive voltage (power supply voltage) of the delay unit DUis preferably set at a value smaller than a sum of a threshold voltageof an N-channel transistor and a threshold voltage of a P-channeltransistor which constitute the CMOS inverter gate circuit, so thatelectric power consumption per delay unit can be very small. Althoughthe delay time of the delay unit DU increases as the drive voltagethereof decreases, this embodiment makes it possible to satisfy both thereduction of power consumption and the high output resolution because ofthe provision of the vernier.

The size of transistors constituting the delay unit DU1 of the firstdelay line 21, and the delay unit DU2 of the second delay line 22 ispreferably larger than twice the size of transistors constituting thedelay unit DU of the pulse delay circuit 11, so that productionvariations in the delay characteristics of the first delay line 21 andthe second delay line 22 become small, to thereby increase the accuracyof the vernier.

Second Embodiment

Next, a second embodiment of the invention is explained. The followingexplanation focuses on a difference between the second embodiment andthe first embodiment, which resides in the structures of theirdigitization sections. FIG. 10 is a block diagram showing the structureof a digitization section 10 a included in a time measuring apparatusaccording to the second embodiment of the invention.

As shown in FIG. 10, the digitization section 10 a is provided with adelay circuit 31 (which may be a single delay unit DU) disposed on asignal path for supplying the measurement signal PB to the interpolationcircuit 14 and the reverse timing extraction circuit 13, and a delaycircuit 32 disposed on a signal path for supplying the measurementsignal PB to the latch/encoder 12 and the latch 16. The delaycharacteristic of the delay circuit 31 with respect to the drive voltageand the temperature is the same as that of the delay units DUconstituting the pulse delay circuit 11. The delay characteristic of thedelay circuit 32 is independent of the drive voltage and thetemperature.

The time measuring apparatus of this embodiment can cancel the variationof the resolution (time width of one LSB) of the output (middle data) ofthe latch/encoder 12 resulting from the variation of the delay time ofthe delay units DU depending on the drive voltage and the temperature,in order to generate the output data DT with a high degree of accuracynot affected by the drive voltage variation and the temperaturevariation.

The delay circuit 32 is for adaptation to the provision of the delaycircuit 31.

Third Embodiment

Next, a third embodiment of the invention is explained. The followingexplanation focuses on a difference between the third embodiment and thefirst embodiment, which resides in the structures of their digitizationsections. FIG. 11 is a block diagram showing a structure of adigitization section 10 b included in a time measuring apparatusaccording to the third embodiment of the invention.

As shown in FIG. 11, the digitization section 10 b includes, instead ofthe latch/encoder 12 and the reverse timing extraction circuit 13, alatch/reverse timing extraction circuit 43, and an encoder 42. Thelatch/reverse timing extraction circuit 43 is configured to latch theoutputs P1 to PL of the delay units DU constituting the pulse delaycircuit 11 at the measurement timing Ti of the measurement signal PB,and generate the reverse timing signal PR representing a timing at whichany one of the outputs P1 to PL of the delay units DU reverses for thefirst time after the measurement signal PB is inputted on the basis ofthe latched outputs P1 to PL. The encoder 42 is configured to outputb-bit digital data (middle data) DM representing in what stage number ofthe delay units DU the pulse signal is on the basis of the outputs P1 toPL latched by the latch/reverse timing extraction circuit 43.

As shown in FIG. 12, the latch/reverse timing extraction circuit 43includes front-side flip-flop circuits DFF, rear-side flip-flop circuitsDFF_E, an OR circuit OR, and a enabling signal generating circuit. Theoutputs of the rear-side flip-flop circuits DFF_E are supplied to theencoder 42 as the latch results LP1 to LPL.

According to this embodiment, the circuit scale of the time measuringapparatus 1 can be made small, because the same latch circuit can beshared in this embodiment, compared to the first embodiment in which thelatch/encoder 12 and the reverse timing extraction circuit 13 have alatch circuit individually. In addition, since the encoder 42, and theOR circuit OR generating the reverse timing signal PR (and consequentlythe interpolation circuit 14) are provided with the output of the samelatch circuit, it is possible to make a point at which the LSB of themiddle data DM generated by the encoder 42 changes coincide with a pointat which the stage-number data changes from DDmin to DDmax (see FIG. 7)in order to improve the accuracy of the lower data DL.

The digitization section 10 b of this embodiment may be provided withthe delay circuits 31, 32 explained in the second embodiment.

Fourth Embodiment

Next, a fourth embodiment of the invention is explained.

The following explanation focuses on a difference between the fourthembodiment and the first embodiment, which resides in the structures oftheir first delay line 21 and second delay line 22, and their vicinity.FIG. 13 is a circuit diagram showing a structure around the first delayline 21 and the second delay line 22.

In this embodiment, the delay characteristic of the delay units DU1constituting the first delay line 21 and that of the delaycharacteristic of the delay units DU2 constituting the second delay line22 are made the same with each other. As shown in FIG. 13, thisembodiment is provided with a D/A converter 34 generating the drivevoltage of the delay units DU1 constituting the first delay line 21 inaccordance with a first delay-setting value stored in a register 33, anda D/A converter 36 generating the drive voltage of the delay units DU2constituting the second delay line 22 in accordance with a seconddelay-setting value stored in a register 35.

The first and second delay-setting values respectively stored in theregisters 33, 35 are set to such values that the D/A converters 34, 36generate the drive voltages which makes the delay time difference ΔTbecomes Td/M.

The first and second delay-setting values may be variably set dependingon the surrounding environment (power supply voltage, ambienttemperature, etc.) According to this embodiment, since the delay timedifference ΔT can be set exactly at Td/M irrespective of productiontolerance, the measurement accuracy can be improved. In addition,according to this embodiment, the accuracy of the interpolation circuit14 can be easily changed by changing the first and second delay-settingvalues.

Incidentally, since the gain error can be made small in this embodiment,the divider 29 provided in the data conversion circuit 26 for correctingthe gain error may be eliminated. Furthermore, since it is not necessaryto allow for margin depending on the gain error in the stage numbers ofthe delay units DU1 constituting the first delay line 21 and the delayunits DU2 constituting the second delay line 22, the circuit scales ofthe first delay line 21 and the second delay line 22 can be reduced.

Fifth Embodiment

Next, a fifth embodiment of the invention is explained.

The following explanation focuses on a difference between the fifthembodiment and the first embodiment, which resides in the structures oftheir interpolation circuits. As shown in FIG. 14, the interpolationcircuit 14 a in this embodiment includes a first delay line 21 aconstituted by the delay units DU1 connected in ring form, and a seconddelay line 22 a constituted by the delay units DU2 connected in ringform.

The flip-flop circuits DFF constituting an edge detection circuit 23 aare applied with the outputs of the delay units DU1 at their data inputterminals, and applied with logical products of the outputs of the delayunits DU2 and a circulation stop signal S (to be explained later) attheir clock input terminals.

An encoder 25 a is configured to change the circulation stop signal Sfrom the high level to the low level upon detecting that any one of theoutputs QV1 to QVP of the flip-flop circuits DFF constituting the edgedetection circuit 23 a reverses (that is, upon detecting the first delaypulse has overtaken the second delay pulse), and generate datarepresenting a position (the stage number of the delay unit DU1, and thedelay unit DU2) of these delay pulses in digitized form when theovertaking has occurred.

This embodiment is further provided with a circulation number counter 41counting the output (the circulating pulse signal) of the final stagedelay unit DU2 of the second delay line 22 a, and a latch circuit 42latching the count value of the circulation number counter 41 at arising edge of the circulation stop signal S outputted from the encoder25 a.

The data conversion circuit 26 generates the stage-number data formed bythe output of the encoder 25 a as its lower bits, and the output of thelatch circuit 42 as its higher bits. According to this embodiment whereeach of the first delay line 21 a and the second delay line 22 a isformed as a ring delay line, it is possible to substantially reduce thenumbers of the delay units DU1 and delay units DU2, to thereby downsizethe interpolation circuit 14 a, and consequently downsize the timemeasuring apparatus 1.

Incidentally, the drive voltage supplied to the delay units DU1constituting the first delay line 21 a, and the delay units DU2constituting the second delay line 22 a may be the analog input signalVin as in the case of the first embodiment, or the output of the D/Aconverter as in the case of the third embodiment.

Sixth Embodiment

Next, a sixth embodiment of the present invention is explained.

In the above, the present invention has been described by way ofexamples where the present invention is applied to the time measuringapparatus, while on the other hand, the present invention is describedbelow by way of an example where the present invention is applied to anA/D converter apparatus 2. FIG. 15A is a block diagram showing anoverall structure of the A/D converter apparatus 2. FIG. 15B is a timingdiagram showing the operation of the A/D converter apparatus 2.

As shown in FIG. 15A, the A/D converter apparatus 2 includes an A/Dconversion control section 4, and a digitization section 10. The A/Dconversion control section 4 is configured to output the start signal PAwhose signal level changes from a non-active level (low level in thisembodiment) to an active level (high level in this embodiment) when thestart command is inputted from outside, and the measurement signal PBwhich rises at constant time intervals after the start timing Ts definedby the start signal PA. The digitization section 10 receives the startsignal PA and the measurement signal PB form the A/D conversion controlsection 4, and outputs the output data DT representing the signal levelof the analog input signal Vin in digitized form at the timing Ti (thatis, at constant time periods) indicated by the measurement signal PB.

The digitization section 10 in this embodiment is identical in structurewith the digitization section 10 in the first embodiment.

It should be noted that the A/D conversion apparatus 2 described abovemay be provided with any one of the configuration explained in thesecond to fourth embodiments.

Seventh Embodiment

Next, a seventh embodiment of the invention is explained.

As shown in FIG. 16, the seventh embodiment is not different from thetime measuring apparatus 1 or the A/D conversion apparatus 2 describedabove, except that it is additionally provided with a calibrationcircuit 5 for automatically renewing the correction data (offset data,division data) stored in the memory 27 of the data conversion circuit26. In FIG. 16, the time measurement control section 3 and the A/Dconversion control section 4 are omitted from illustration.

The calibration circuit 5 includes a test signal generating section 6,and a correction data calculation/write section 7. The test signalgenerating section 6 is for supplying the digitization section 10 withthe analog input signal Vin, start signal PA, and measurement signal PBfor test use. The correction data calculation/write section 7 operatesto calculate the correction data from the data which the digitizationsection 10 generates in accordance with the signals supplied from thetest signal generating section 6, and renew the contents of the memory27 by the calculated correction data.

More specifically, the test signal generating section 6 supplies thedigitization section 10 with the analog input signal Vin of a constantvoltage for a predetermined time period when it receives the startcommand from outside. In this state, the test signal generating section6 starts the pulse delay circuit 11 by supplying it with the startsignal PA, and thereafter supplies it with the measurement signal PBwhose period is modulated so that the temporal relationship between themeasurement timings and the reverse timings changes variously.

The correction data calculation/write section 7 takes in thestage-number data DD generated by the encoder 25 of the lower codingsection 24 each time the measurement signal PB is inputted thereto.Since the period of the measurement signal PB is modulated, andaccordingly the temporal relationship between the measurement timing andthe reverse timing changes variously, a group of the stage-number dataDD as shown in FIG. 7 is obtained.

The correction data calculation/write section 7 extracts, from theobtained group of the stage-number data DD, its maximum value DDmax andits minimum value DDmin, and stores these values as the offset data,together with the difference therebetween (DDmax−DDmin) as the divisiondata in the memory 27.

According to this embodiment where the correction data (offset data,division data) necessary for the interpolation circuit 14 to generatethe lower data DL can be renewed as necessary, it is possible to alwayskeep the degree of accuracy of the lower data DL at high level.

Other Embodiments

Although the pulse delay circuit 11 has been described as beingconstituted by the delay units DU connected in ring form in the aboveembodiments, it may be constituted by a series connection of the delayunits DU. In this case, the circulation number counter 15 and the latchcircuit 16 can be removed.

In the above embodiments, the flip-flop circuits DFF constituting theedge detection circuit 23 are applied with the outputs of the delayunits DU1 at their data input terminals, and applied with the outputs ofthe delay units DU2 at their clock input terminals, they may be appliedwith the outputs of the delay units DU2 at their data input terminals,and applied with the outputs of the delay units DU1 at their clock inputterminals.

In the above embodiments, the delay unit DU is constituted by a seriesconnection of two CMOS inverter gate circuits, it may be constituted bya series connection of three or more CMOS inverter gate circuits. Forexample, it may be constituted by a series connection of four CMOSinverter gate circuits as shown in (b) of FIG. 16, or by a seriesconnection of eight CMOS inverter gate circuits as shown in (c) of FIG.16.

The unit-to-unit variation of the delay time of the delay unit DUdecreases as the number of the CMOS inverter gate circuits constitutingthe delay unit DU increases. Accordingly, it is possible to improve theaccuracy of digitization by increasing the number of the CMOS invertergate circuits constituting one delay unit DU.

The above explained preferred embodiments are exemplary of the inventionof the present application which is described solely by the claimsappended below. It should be understood that modifications of thepreferred embodiments may be made as would occur to one of skill in theart.

1. A digitization apparatus comprising: a pulse delay circuitconstituted by a plurality of pulse delay units connected in series orin ring form, each of said pulse delay units having a delay timedepending on a voltage level of an analog input signal applied theretoas a drive voltage thereof, said pulse delay circuit allowing a pulsesignal to travel through said pulse delay units while being successivelydelayed by said delay time; a higher coding circuit generating, uponreceiving a measurement signal indicating a measurement timing fromoutside, digitized data representing the number of said pulse delayunits which said pulse signal has passed; a reverse timing extractioncircuit extracting a timing, as a reverse timing signal, at which anyone of said pulse delay units has reversed in output level for the firsttime after said measurement timing; a first delay line constituted by aplurality of first delay units connected in series or in ring form, eachof said first delay units having a first delay time, said first delayline allowing said reverse timing signal to travel through said firstdelay units while being successively delayed by said first delay time; asecond delay line constituted by a plurality of second delay unitsconnected in series or in ring form, each of said second delay unitshaving a second delay time larger than said first delay time by 1/M (Mbeing an integer not smaller than 2) of said delay time of said pulsedelay units, said first delay line allowing said reverse timing signalto travel through said second delay units while being successivelydelayed by said second delay time; and a lower coding circuit generatingdigitized data representing a time difference between said measurementtiming and said reverse timing on the basis of the number of said firstdelay units which said reverse timing signal has passed when said numberof said first delay units has overtaken the number of said second delayunits which said measurement signal has passed; said digitizationapparatus outputting data formed by said digitized data generated bysaid higher coding circuit as higher bits thereof, and said digitizeddata generated by said lower coding circuit as lower bits thereof. 2.The digitization apparatus according to claim 1, wherein said firstdelay units and said second delay units are applied with said analoginput signal as a drive voltage thereof.
 3. The digitization apparatusaccording to claim 1, wherein said M is a power of
 2. 4. Thedigitization apparatus according to claim 1 further comprising a timemeasurement control apparatus generating a constant voltage signal assaid analog input signal, and a start signal to cause said pulse signalto start traveling through said pulse delay units of said pulse delaycircuit, said digitization apparatus outputting data representing indigitized form a time interval between a start timing indicated by saidstart signal and said measurement timing each time said measurementsignal is inputted to said higher coding circuit.
 5. The digitizationapparatus according to claim 1 further comprising an A/D conversioncontrol circuit supplying said higher coding circuit with saidmeasurement signal at predetermined constant periods, said digitizationapparatus outputting, at said measurement timing indicated bymeasurement signal, data representing a voltage level of said analoginput signal in digitized form.
 6. The digitization apparatus accordingto claim 5 further comprising a differential calculating circuitsuccessively memorizing output data generated by said digitizationapparatus, and calculating a difference between said output datagenerated previous time and said output data generated this time.
 7. Thedigitization apparatus according to claim 1, wherein said lower codingcircuit includes an edge detection circuit constituted by a plurality offlip-flop circuits provided in one-to-one relationship with said firstdelay units and said second delay units, each said flip-flop circuitreceiving an output of a corresponding one of said first delay units atone of a data input terminal and a clock input terminal thereof, andreceiving an output of a corresponding one of said second delay units atthe other of said data input terminal and said clock input terminalthereof, an encoder generating stage-number data representing indigitized form a stage number of one of said flip-flop circuits whichhas changed an output level thereof, and a data conversion circuitconverting said stage-number data to such data whose value monotonouslyincreases with increase of a time difference between said reverse timingand said measurement timing.
 8. The digitization apparatus according toclaim 7, wherein said data conversion circuit performs at least one ofelimination of offset contained in said stage-number data, andcorrection of a gain error of said stage-number data.
 9. Thedigitization apparatus according to claim 8, further comprising a testsignal generating circuit having a function of generating said analoginput signal, and generating said measurement signal in continuouslychanging period, and a correction data calculating circuit calculatingcorrection data needed for said data conversion circuit to performelimination of said offset or correction of said gain error on the basisof said stage-number data outputted from said encoder when saiddigitization apparatus operates on said analog input signal, and saidmeasurement signal generated by said test signal generating circuit. 10.The digitization apparatus according to claim 1, wherein a delay circuithaving the same characteristic with respect to at least one of drivevoltage and ambient temperature with said pulse delay units is providedin an input side of said second delay line.
 11. The digitizationapparatus according to claim 1, further comprising a first D/A convertergenerating, from adjustable digital set value, an adjustable drivevoltage to be supplied to said first delay units, and a second D/Aconverter generating, from adjustable digital set value, an adjustabledrive voltage to be supplied to said second delay units.
 12. Thedigitization apparatus according to claim 1, wherein each said pulsedelay unit is constituted by a series connection of a plurality ofinverter gate circuits.
 13. The digitization apparatus according toclaim 12, wherein each said inverter gate circuit is a CMOS invertergate circuit, said drive voltage of said pulse delay unit is set at avalue smaller than a sum of a threshold voltage of an N-channeltransistor and a threshold voltage of a P-channel transistor, whichconstitute said CMOS inverter gate circuit.
 14. The digitizationapparatus according to claim 1, wherein a size of transistorsconstituting each of said first deadly units and said second delay unitsis larger than twice a size of transistors constituting each of saiddelay units constituting said pulse delay circuit.
 15. The digitizationapparatus according to claim 1, wherein said reverse timing extractioncircuit includes latch circuits latching said measurement signalrespectively in synchronization with outputs of said pulse delay unitsconstituting said pulse delay circuit, and an OR circuit outputting alogical sum of outputs of said latch circuits as said reverse timingsignal.